RNA Molecular Weight Calculator
Paste a transcript, weigh it: the A-C-G-U alphabet, the 5′-triphosphate convention and GC content — RNA’s own table, shown working.
RNA Molecular Weight Calculator
Results recalculate instantly on every keystroke. Nothing you type is transmitted.
What this result does not account for
- Unmodified A-C-G-U sequences only
- Triphosphate convention — synthesized oligos print lower
In short: AUG — the start codon — prices at 1,139.590000 Da: adenine 329.21, guanine 345.21, uracil 306.17, plus the 159.000000 5′-triphosphate that the convention carries. That phosphate is the whole story of this table: freshly transcribed RNA starts with a triphosphate, and a synthesized oligo without one prints 980.590000. GC content is 66.666667% — two of three bases. The stop codon UAA weighs 1,123.590000: lighter by one guanine, heavier by a second adenine.
Formula
MW = A·329.21 + U·306.17 + C·305.18 + G·345.21 + 159.0 · the +159.0 is the 5′-triphosphate convention
RNA weighs differently from DNA twice over: uracil replaces thymine, and the table’s convention carries a 5′-triphosphate — the state of a freshly transcribed molecule — worth 159.000000 on every transcript. Nucleotide monophosphate masses are conventional table values, quoted approximate. There is no double-strand road here on purpose: structured RNA folds back on itself in ways no simple complement prices.
Worked Example
- Paste the transcript — T is refused; RNA spells uracil as U.
- Read the mass with the triphosphate convention applied.
- Read the no-phosphate figure for synthesized oligos.
- Check GC content and the per-base counts.
Defaults: AUG → 1,139.590000 Da with the triphosphate, 980.590000 without. UAA → 1,123.590000. GCAU → four distinct bases, GC 50.000000%.
Strengths & Limits Of This Model
Where this engine is strong
- Both phosphate states printed
- T refused with the position named
Where it stops
- No secondary-structure pricing
- No caps or modified bases
Practical Use Cases
Transcript loggers
mass of an in-vitro transcript
siRNA ordering
the no-phosphate figure
Teaching
why U and the triphosphate matter
Methodology & Editorial Standards
Computation runs in IEEE-754 double precision at full internal precision; rounding to two decimal places occurs strictly at the display layer, so no cumulative drift enters the result. All monetary outputs use accounting presentation — grouped thousands, two decimals, negatives in parentheses — so figures can be transcribed directly into a model or working paper. Division-by-zero and out-of-domain inputs return an em-dash rather than a misleading number.
This engine was reconciled against an independent reference implementation and hand-verified for the worked example above before release. Our full five-stage review process is published on the About Us page.
Disclaimer. This calculator is provided for informational and modelling purposes only and does not constitute financial, tax, legal, medical, or engineering advice. Verify all figures with a qualified professional before acting on them.
RNA Molecular Weight Calculator — 8 Expert FAQs
8 analyst-written answers to the questions practitioners actually ask — optimised for voice and answer-engine retrieval.
Why is there a plus 159 in the formula?
Because the convention answers a question about state: transcripts made by polymerase start with a 5′-triphosphate, and the table weighs that molecule. Chemically synthesized RNA usually lacks it. The page prints both figures so neither state is guessed.
Why is T refused instead of corrected?
Because T is not a typo in any alphabet but the wrong one: a T in an RNA box usually means a DNA sequence wandered in. The refusal names the letter and the position and points at the DNA page, where thymine is priced honestly, rather than silently substituting 306.17 for 304.2.
Where is the double-strand card?
Deliberately absent. RNA’s secondary structure pairs bases within one strand — hairpins, loops, stems — and a naive complement doubling would price a molecule that exists only in textbooks. Transcript mass is a single-strand question; the DNA page owns the duplex road.
Why do the masses differ from DNA’s per-base table?
Two reasons, both chemical: uracil lacks DNA’s methyl group (306.17 against thymine’s 304.2), and the ribose’s extra oxygen adds 16 to every base — adenine 329.21 against 313.21. Same letters, different sugar.
What about capped or modified RNA?
Outside the honest table: caps, pseudouridines, methylations and phosphorothioates each shift the mass, and a four-letter table cannot price them without pretending. The page refuses unknown letters by position so a modification code surfaces instead of vanishing into a plausible number.
Why print both triphosphate states?
Because the two RNAs are different molecules: a transcript made by polymerase opens with a 5′-triphosphate and the +159.000000 convention prices it; a chemically synthesized oligo carries a hydroxyl and prints 159.000000 lower. Ordering labels, yield calculations and ligation plans all care which one you mean — the card makes the choice explicit instead of burying it in a formula.
What does the GC card count on an RNA page?
The same letters it does on DNA — guanine and cytosine — over the typed length, with all four counts printed. For AUG that is 2 of 3, 66.666667%; for a full transcript the percentage is the fastest sanity check that the paste is the molecule you meant, before the mass goes anywhere near an order form.
How is this different from the protein page?
Alphabet size and convention. Twenty letters with a per-residue itemised bill and one terminal water on the protein page; four letters and a 159.000000 triphosphate convention here. Both are the same discipline — count, weigh, show the adjustment — on different chemistries.